Glass ceramic mass and use thereof

ABSTRACT

The invention relates to a glass ceramic mass containing at least one oxide ceramic containing barium, titanium and at least one rare earth metal Rek; and at least one glass material containing at least one oxide with boron, at least one oxide with silicon and at least one oxide with at least one bivalent metal Me2+. The glass ceramic mass is characterised in that the glass material contains at least one oxide with bismuth, especially bismuth trioxide. The oxide ceramic is especially a microwave ceramic of formula BaRek2Ti4O12, Rek being neodymium or samarium. The composition of the oxide ceramic remains essentially constant during the sintering of the glass ceramic, enabling the material properties of the glass ceramic mass, such as permittivity (20-80), quality (800-5000) and Tkf (±20 ppm/K) to be specifically predetermined. The glass ceramic mass is characterised by a densification temperature of under 910 ° C. and can is therefore suitable for use in LTCC (low temperature cofired ceramics) technology, for integrating a passive electrical component in the volume of a multilayered ceramic body. Silver in particular can be used as an electroconductive material in this case.

[0001] The invention relates to a glass ceramic mass, comprising atleast one oxide ceramic, containing barium, titanium and at least onerare earth metal Rek and at least one glass material, containing atleast one oxide with boron, at least one oxide with silicon and at leastone oxide with at least one bivalent metal Me2+. In addition to theglass ceramic mass, an application of the glass ceramic mass isdescribed. A glass ceramic mass of the aforementioned type is known fromU.S. Pat. No. 5,264,403. The oxide ceramic for the known glass ceramicmass is manufactured from barium oxide (BaO), titanium dioxide (TiO₂), atrioxide of a rare earth metal (Rek₂O₃) and possibly bismuth trioxide(Bi₂O₃). The rare earth metal Rek is for example neodymium. The glassmaterial in the glass ceramic mass consists of boron trioxide (B₂O₃),silicon dioxide and zinc oxide (ZnO). A ceramic proportion of the oxideceramic in the glass ceramic mass is for example 90% and a glassproportion of the glass material 10%.

[0002] A compression of the glass ceramic mass occurs at a sinteringtemperature of about 950° C. The glass ceramic mass is thus suitable foruse in LTCC (low temperature cofired ceramics) technology. The LTCCtechnology is described for example in D. L. Wilcox et al, Proc.1997ISAM, Philadelphia, pp. 17 to 23. The LTCC technology is a ceramicmultilayer method in which a passive electrical component can beintegrated in the volume of a ceramic multilayer body. The passiveelectrical component is for example an electrical conductor track, acoil, an induction or a capacitor. Integration is achieved, for example,by printing a metal structure corresponding to the component on one ormore ceramic film blanks, stacking the printed ceramic film blanks aboveone another to form a composite and sintering the composite. Sinceceramic film blanks are used with a low sintering glass ceramic mass,electrically highly conductive elementary metal Me0 with a low meltingpoint such as silver or copper can be sintered in a composite with theceramic film blank. In this situation, the functional integrity of thecomponent integrated through the use of LTCC technology is cruciallydependent on the dielectric material properties of the glass ceramicused. A material property of this type is for example the permittivity(ε_(r)), a quality factor (Q) and a temperature coefficient of frequency(Tf value).

[0003] With regard to the known glass ceramic mass, the glass proportionis relatively low, with the result that compression of the glass ceramicmass takes places as a result of reactive liquid phase sintering. Duringthe sintering process, a liquid glass phase (glass melt) is formed fromthe glass material. At a higher temperature the oxide ceramic dissolvesin the glass melt until a saturation concentration is reached and aseparation of the oxide ceramic occurs once again. As a result of theoxide ceramic dissolving and separating out again, the composition ofthe oxide ceramic and thus also the composition of the glass phase orthe glass material can change. During cooling, crystallization from theglass melt can additionally occur. For example, in this situation oneconstituent of the oxide ceramic remains in the glass phase aftercooling of the glass ceramic mass. If the composition of the oxideceramic and thus also the composition of the glass material changes as aresult of compression, it is difficult to define the material.properties of the compressed glass ceramic mass and thus to guaranteethe functional integrity of the component integrated through the use ofLTCC technology.

[0004] The object of the present invention is to specify a glass ceramicmass with an oxide ceramic, whose composition remains essentiallyunchanged during a sintering process.

[0005] This object is achieved by specifying a glass ceramic masscomprising at least one oxide ceramic, containing barium, titanium andat least one rare earth metal Rek and at least one glass material,containing at least one oxide with boron, at least one oxide withsilicon and at least one oxide with at least one bivalent metal Me2+.The glass ceramic mass is characterized by the fact that the glassmaterial contains at least one oxide with bismuth.

[0006] The glass ceramic mass is a glass ceramic compound and isindependent of its state. The glass ceramic mass can exist as a ceramicgreen body. With regard to a green body, a film blank for example, apowder of the oxide ceramic and a powder of the glass material can becombined with one another by means of an organic binding. agent. It isalso. conceivable that the glass ceramic mass can exist as a powdermixture of the oxide ceramic and the glass material. Furthermore, theglass ceramic mass can exist as a sintered ceramic body. For example, aceramic multilayer body produced in a sintering process consists of theglass ceramic mass. This ceramic multilayer body can be submitted to afurther sintering process.

[0007] The oxide ceramic can be present as a single phase. However, itcan also consist of a plurality of phases. It is conceivable, forexample, for the oxide ceramic to consist of phases each having adiffering composition. The oxide ceramic is thus a mixture of differentoxide ceramics. It is also conceivable for one or more parent compoundsof an oxide ceramic to be present which are then converted to form theactual oxide ceramic only during the sintering process.

[0008] The glass material can likewise be a single phase. For example,the phase is a glass melt consisting of boron trioxide, silicon dioxide,zinc oxide and bismuth trioxide. It is also conceivable for the glassmaterial to consist of a plurality of phases. For example, the glassmaterial consists of a powder mixture of the specified oxides. A jointglass melt is formed from the oxides during the sintering process. It isalso conceivable for the glass material to be a crystallization productof the glass melt. This means that the glass material is present notonly as a glass melt after the sintering process but can also be presentin a crystalline form.

[0009] The fundamental concept of the present invention consists inusing a bismuth oxide, in particular bismuth trioxide, in the glassmaterial. One advantage in doing so consists in the fact that asoftening temperature T_(soft) of the glass material can be lowered. Thelower the glass transition point, the lower is the sintering temperatureor a vitrification temperature for the corresponding glass ceramic mass.At the vitrification temperature, almost complete compression of theglass ceramic mass can be achieved in a short time.

[0010] In addition, bismuth trioxide influences the way in which theoxide ceramic dissolves and separates out again in the glass melt duringthe sintering process in a particularly advantageous manner (for exampleas a result of the lower vitrification temperature). Practically noeluation of individual components of the oxide ceramic occurs. Thecomposition of the oxide ceramic either does not change or changes onlyslightly and can therefore be very well predetermined.

[0011] It is known that bismuth which is present: in the. oxide ceramicreacts with elementary silver at an elevated temperature. With regard tothe use of an oxide ceramic containing bismuth in LTCC technology inconjunction with the use of silver as an electrically conductingmaterial, this combination can result in an undesired reaction impairingthe functional integrity of the component which is to be manufactured.If the glass material contains bismuth trioxide, the vitrificationtemperature is reduced. A sintering process can take place at lowertemperatures. In this way, a reaction between bismuth, or bismuthtrioxide, and elementary silver can be suppressed. Furthermore, if theglass proportion is relatively low, relatively little bismuth is alsopresent, with the result that no noticeable reaction occurs betweenbismuth and silver.

[0012] In a special embodiment, the oxide ceramic has a formalcomposition BaRek₂Ti₄O₁₂. The oxide ceramic having the aforementionedcomposition is referred to as microwave ceramic since its materialproperties (permittivity, quality, Tf value) are very well suited foruse in microwave technology.

[0013] In particular, the glass material contains at least one oxidewith at least one rare earth metal Reg. The rare earth metal Reg ispresent for example as the trioxide Reg₂O₃. By using the oxide of therare earth metal Reg, it is possible match the permittivity of the glassmaterial, which contributes to the permittivity of the overall glassceramic mass, to the permittivity of the oxide ceramic. A glass ceramicmass exhibiting a permittivity of 20 to 80 or even higher is thusaccessible.

[0014] In particular, the rare earth metal Rek and/or the rare earthmetal Reg from the group comprising lanthanum and/or neodymium and/orsamarium are selected. Other lanthanides or even actinides are alsoconceivable. The rare earth metals Rek and Reg can be identical, but canalso be different rare earth metals.

[0015] In a special embodiment, the oxide ceramic contains the bivalentmetal Me2+. In particular, the bivalent metal Me2+ is selected from thegroup comprising beryllium, magnesium, calcium, strontium, barium,copper and/or zinc. The bivalent metal Me2+ can be present as a separateoxidic phase. In particular, the bivalent metal Me2+ is a doping of theoxide ceramic. In the oxide ceramic, the bivalent metal Me2+ causes asignificant reduction in the sintering temperature of the oxide ceramic.Furthermore, it is possible to control the dielectric materialproperties of the oxide ceramic. For example, the oxide ceramic havingthe composition BaRek₂Ti₄O₁₂ is doped with zinc. Like the oxide ofbismuth, the bivalent metal Me2+ can bring about a suppression of theeluation of individual components of the oxide ceramic during thesintering process. It has become apparent that it is particularlyadvantageous if the oxide ceramic is doped with the bivalent metal Me2+which also occurs in the glass material. In particular, zinc is to bementioned here as a bivalent metal Me2+. Zinc has a particularlyadvantageous effect on reactive liquid phase sintering and on anyprocess of dissolving and separating out again which occurs in thissituation.

[0016] In a further embodiment, in addition to the oxide of silicon theglass material contains as a tetravalent metal at least one oxide of atleast one further tetravalent metal Me4+. In addition to the silicondioxide, the glass material contains at least one further dioxide of atetravalent metal. The further tetravalent metal Me4+ is selected inparticular from the group comprising germanium and/or tin and/ortitanium and/or zirconium. In addition to silicon dioxide, the oxides ofthe aforementioned tetravalent metals support a glassiness of the glassmaterial. This means that these oxides are used, as incidentally arealso the oxides of the aforementioned bivalent metals Me2+, to control aviscosity temperature characteristic of the glass material. For example,the softening temperature T_(Soft) of glass material can be set.Crystallization of the glass material can likewise be influenced.

[0017] In a special embodiment, 100% by volume of the glass ceramic massis composed of a ceramic proportion of the oxide ceramic which isselected from the range between 70% by volume inclusive to 95% by volumeinclusive, and a glass proportion of the glass material which isselected from the range between 30% by volume inclusive to 5% by volumeinclusive. If the glass ceramic mass is subjected to a sinteringprocess, the aforementioned reactive liquid phase sintering takes place.In the case of particularly advantageous behavior with respect to anyprocess of dissolving and separating out again, as is the situation inparticular when the bivalent metal occurs in the oxide ceramic and inthe glass material, it is also possible to keep the glass proportionbelow 5% by volume.

[0018] In particular, the oxide ceramic and/or the glass materialcontain a powder with a mean particle size (D₅₀ value) which is selectedfrom the range between 0.1 μm inclusive and 1.5 μm inclusive. The meanparticle size is also referred to as half-value particle size. In orderto maintain a very low glass proportion without restricting any processof dissolving and separating out again, powders having the specifiedparticle sizes are particularly advantageous. The powders have a largereactive surface which is necessary for the reactive liquid phasesintering process.

[0019] Normally, in order to reduce the sintering temperature and toincrease the permittivity of the glass ceramic mass, lead oxide (PbO) isadded to the glass material. With regard to the present invention, thelead oxide proportion and/or cadmium oxide proportion of the glassceramic mass and/or of the oxide ceramic and/or of the glass material isa maximum 0.1%, in particular a maximum of 1 ppm. By preference, withregard to environmental considerations, the proportion of lead oxide andcadmium oxide is almost zero. This is achieved by the present inventionwithout significant restriction of the material properties of the glassceramic mass.

[0020] In a special embodiment, the ceramic mass exhibits a maximumvitrification temperature of 950° C., and in particular a maximum of910° C. or 890° C. In this situation, in particular, a glass ceramicmass is accessible with a permittivity which is selected from the rangebetween 20 inclusive and 80 inclusive, a quality which is selected fromthe range between 800 inclusive and 5000 inclusive, and a Tf value whichis selected from the range between −20 ppm/K inclusive and +20 ppm/Kinclusive. With these material properties, the glass ceramic mass isvery well suited for use in microwave technology.

[0021] According to a second aspect of the invention, a ceramic bodyusing a previously described glass ceramic mass is specified. Inparticular, the ceramic body has at least one elementary metal Me0 whichis selected from the group comprising gold and/or silver and/or copper.By preference, the ceramic body is a ceramic multilayer body. Thepreviously described glass ceramic mass is used to manufacture theceramic body. As a result of using glass material containing bismuth,vitrification of the glass ceramic mass can already take place below890° C. With regard to a firing process in the presence of elementarysilver, no disruptive interdiffusion occurs. In particular, a ceramicbody in the form of a ceramic multilayer body can be manufactured inthis manner. The glass ceramic mass is used in particular in ceramicfilm blanks in LTCC technology. In this way, glass ceramic masses aremade available to the LTCC technology, having excellent materialproperties for the manufacture of microwave technology components.

[0022] To summarize, the following advantages result from the invention:

[0023] The composition of the oxide ceramic remains essentially constantduring sintering of the glass ceramic mass. The material properties ofthe glass ceramic mass can thus be pre-set in a defined manner.

[0024] Almost complete compression (vitrification) of the glass ceramicmass is possible at a temperature of below 910° C., and even below 890°C.

[0025] By means of suitable (oxidic) additions to the oxide ceramic andto the glass material, the sintering behavior of the glass ceramic massand the material properties of the glass ceramic mass can be setspecifically and almost as desired. It is thus possible, for example, toset permittivity, quality and Tf value over a wide range in each casewhilst retaining a low vitrification temperature. Compression isachieved without the use of lead oxide and/or cadmium oxide.

[0026] The invention will be described in the following with referenceto an embodiment and the associated drawing. The drawing shows aschematic cross-section, not to scale, of a ceramic body with the glassceramic mass in a multilayer construction.

[0027] According to the embodiment, the glass ceramic mass 11 is apowder consisting of an oxide ceramic and a powder of a glass material.The oxide ceramic has the formal composition BaRek₂Ti₄O₁₂. The rareearth metal is neodymium. The oxide ceramic is doped with a bivalentmetal Me2+ in the form of zinc. In order to manufacture the oxideceramic, appropriate quantities of barium oxide, titanium dioxide andneodymium trioxide are mixed together with approximately one % by weightzinc oxide, calcinated or sintered, and subsequently ground to producethe corresponding powder.

[0028] The glass material contains boron, bismuth, silicon and zinc. Theglass material is characterized by the following composition: 27.5 mol %boron trioxide, 34.8 mol % bismuth oxide, 32.5 mol % zinc oxide and 6mol % silicon dioxide.

[0029] 100% by volume of the glass ceramic mass is composed of 90% byvolume of the ceramic material and 10% by volume of the glass material.Ceramic material and glass material have a D₅₀ value of 0.8 μm. Thevitrification temperature of the glass ceramic mass is 900° C. Thepermittivity of the glass ceramic mass is 64, the quality is 820, andthe Tf value is 4 ppm/K.

[0030] The glass ceramic mass 11 described is used in order to integratea passive electrical component 6, 7 in the volume of a ceramicmultilayer body 1 with the aid of LTCC technology. The ceramicmultilayer body 1 produced in this manner has ceramic layers 3 and 4which are produced from ceramic film blanks together with the glassceramic mass 11. The ceramic layers 2 and 5 have a further glass ceramicmass 12 which is different from the glass ceramic mass 11. Theelectrically conductive material comprising the electronic components isan elementary metal Me0 in the form of silver.

1. Glass ceramic mass comprising at least one oxide ceramic, containingbarium, titanium and at least one rare earth metal Rek, and at least oneglass material, containing at least one oxide with boron, at least oneoxide with silicon and at least one oxide with at least one bivalentmetal Me2+, characterized in that the glass material contains at leastone oxide with bismuth.
 2. Glass ceramic mass according to claim 1,whereby the oxide ceramic has a formal composition BaRek₂Ti₄O₁₂. 3.Glass ceramic mass according to claim 1 or 2, whereby the glass materialcontains at least one oxide with at least one rare earth metal Reg. 4.Glass ceramic mass according to one of claims 1 through 3, whereby therare earth metal Rek and/or the rare earth metal Reg is selected fromthe group comprising lanthanum and/or neodymium and/or samarium. 5.Glass ceramic mass according to one of claims 1 through 4, whereby theoxide ceramic contains the bivalent metal Me2+.
 6. Glass ceramic massaccording to one of claims 1 through 5, whereby the bivalent metal Me2+is selected from the group comprising beryllium, magnesium, calcium,strontium, barium, copper and/or zinc.
 7. Glass ceramic mass accordingto one of claims 1 through 6, whereby in addition to the oxide ofsilicon the glass material contains as a tetravalent metal at least oneoxide with at least one further tetravalent metal Me4+.
 8. Glass ceramicmass according to claim 7, whereby the further tetravalent metal Me4+ isselected from the group comprising germanium and/or tin and/or titaniumand/or zirconium.
 9. Glass ceramic mass according to one of claims 1through 8, whereby 100% by volume of the glass ceramic mass is composedof a ceramic proportion of the oxide ceramic which .is selected from therange between 70% by volume inclusive to 95% by volume inclusive, and aglass proportion of the glass material which is selected from the rangebetween 30% by volume inclusive to 5% by volume inclusive.
 10. Glassceramic mass according to one of claims 1 through 9, whereby the oxideceramic and/or the glass material contain a powder with a mean particlesize which is selected from the range between 0.1 μm inclusive and 1.5μm inclusive.
 11. Glass ceramic mass according to one of claims 1through 10, whereby a lead oxide proportion and/or a cadmium oxideproportion of the glass ceramic mass and/or of the oxide ceramic and/orof the glass material is a maximum 0.1%, in particular a maximum of 1ppm.
 12. Glass ceramic mass according to one of claims 1 through 11,with a maximum vitrification temperature of 950° C., in particular amaximum of 890° C.
 13. Glass ceramic mass according to claim 12, with apermittivity which is selected from the range between 20 inclusive and80 inclusive, a quality which is selected from the range between 800inclusive and 5000 inclusive, and a Tf value which is selected from therange between −20 ppm/K inclusive and +20 ppm/K inclusive.
 14. Ceramicbody using a glass ceramic mass according to one of claims 1 through 13.15. Ceramic body according to claim 14, with at least one elementarymetal Me0 which is selected from the group comprising gold and/or silverand/or copper.
 16. Ceramic body according to claim 13 or 14, whereby theceramic body is a ceramic multilayer body.